Paleobotanical records and molecular data from modern forests can provide a synergistic
understanding of the ecological and evolutionary history of an organism. I used the fossil
record to generate hypotheses that I tested with statistical phylogeographic methods for
Douglas-fir (Pseudotsuga menziesii). In Chapter 1, I describe alternative scenarios of
glacial refugia and postglacial migration based on compiled fossil pollen and macrofossil
evidence from the late Quaternary. In Chapter 2, I test those hypotheses using coalescent
analyses of mitochondrial and chloroplast DNA sequence data. I also test the
paleobotanical hypothesis that Douglas-fir’s two varieties diverged coincident with the
Cascade orogeny in the late Pliocene. Finally in Chapter 3, I test whether Mexican
Douglas-fir diverged from U.S. populations in the Miocene or Pleistocene, consistent
with alternative interpretations of limited fossil evidence in the region. The present
patterns of molecular variation in Douglas-fir are well-described by Pliocene (or early
Pleistocene) divergence of its varieties, mid-Pleistocene colonization of Mexico, and
restriction to multiple glacial refugia in the late Quaternary. Holocene expansion into
Canada resulted in recontact among varieties and hybridization driven entirely by pollen
dispersal but not seed dispersal. Douglas-fir populations have responded
individualistically to past climatic and geologic change, such that some underwent
expansions while others contracted to higher elevation and some diverged while others
coalesced. These findings highlight the complementary insights that fossil and molecular
data provide and can be used to inform the conservation and taxonomy of Douglas-fir.
University of Minnesota Ph.D. dissertation. June 2010. Major: Ecology, Evolution and Behavior. Advisors Jeannine Cavender-Bares, Shinya Sugita. 1 computer file (PDF), vi, 130 pages, ill. (some col.) + 9 supplemental files (4 figures (TIFF), 4 tables (XLSX), 1 table (DOCX))
Gugger, Paul Francis.
Phylogeography of Douglas-fir: testing hypotheses from the fossil record..
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